KR100612153B1 - Apparatus for estimating frequency offset in wireless packet communication system and method thereof - Google Patents

Abstract

The present invention relates to an apparatus and method for frequency offset estimation for a short range wireless packet communication system. In the frequency offset estimation apparatus and method for frequency offset estimation for a CCK wireless LAN system, first, a plurality of symbols are extracted for each corresponding path from a signal received in a multipath, and estimated according to the estimated phase difference between the extracted adjacent symbols. Coarse compensation is performed on the received signal with the frequency offset. Thereafter, a plurality of symbols are extracted for each corresponding path from a signal that is approximately compensated for the frequency offset, and the approximately frequency offset is compensated with a frequency offset estimated according to the estimated phase difference between adjacent symbols by the number of phase difference symbol estimation intervals. Perform fine compensation on the signal. According to the present invention, performance can be maintained in the accurate signal demodulation process in the receiver of the CCK-type wireless LAN system, and the complexity of the implementation can be simplified.

Wireless communication system, frequency offset estimation, CCK, coarse estimation, fine estimation, short range wireless packet communication system

Description

Apparatus and method for frequency offset estimation for short range wireless packet communication system {APPARATUS FOR ESTIMATING FREQUENCY OFFSET IN WIRELESS PACKET COMMUNICATION SYSTEM AND METHOD THEREOF}

1 is a view for explaining the structure and position of the demodulator structure and the frequency offset estimator in a wireless LAN system of the CCK (Complementary Code Keying) method according to an embodiment of the present invention.

2 is a diagram illustrating a received signal model based on a frequency offset in consideration of a transmission signal and a channel according to an embodiment of the present invention.

3 is a diagram illustrating a structure of a frequency offset estimator for a CCK wireless LAN system according to an embodiment of the present invention.

4 is a performance analysis diagram of a frequency offset estimation algorithm for a CCK wireless LAN system according to an embodiment of the present invention.

The present invention relates to an apparatus and method for frequency offset estimation for a short range wireless packet communication system. More specifically, the present invention relates to a frequency offset of two stages consisting of rough estimation and fine estimation in a wireless LAN system of CCK (Complementary Code Keying). An apparatus and method for estimating a frequency offset in an estimation method.

Wireless communication is rapidly evolving in recent years due to user mobility, system flexibility, frequency free use and high speed data transmission. Wireless systems can be classified into LANs and WANs according to their range of use. Recently, the spread of laptops and PDAs (Personal Digital Assistants) has increased the need for wireless LANs. HiperLAN (High Performance Local Area Network) series established in Europe in 1992 as a standard for wireless LAN and IEEE 802.11 series which have been evolving to 802.11b, 802.11a, and 802.11g since the IEEE final draft was approved in 1997. .

The IEEE 802.11 series is emerging as a standard for wireless LAN products by sharing a medium access control (MAC) layer and supporting various data rates for multimedia services. The 802.11b specification is the single-carrier system that supports up to 11 Mbps using Direct Sequence Spread Spectrum (DSSS) and Complementary Code Keying (CCK) in the 2.4 ㎓ ISM band. a is a multi-carrier system supporting various data rates of up to 54 Mbps by applying Orthogonal Frequency Division Multiplexing (OFDM) in the 5 GHz U-NII band. The 802.11g standard, currently under discussion, can be viewed as a baseband aspect that incorporates the features of 802.11 DSSS, 802.11b, and 802.11a. In other words, 2.4GHz ISM band is used for compatibility with 802.11b, DSSS, CCK, PBCC, OFDM, DSSS-OFDM, etc. are supported as transmission mode, and 54Mbps high speed data transmission is possible.

While much discussion is underway today on whether 802.11a or 802.11g will be the next-generation high-speed wireless LAN standard, many studies have anticipated 802.11g, which has advantages in compatibility with 802.11b, the mainstream of wireless LAN. It's going on.

On the other hand, as a prior art, in 1995, a paper entitled "BER Sensitivity of OFDM systems to carrier frequency offset and Wiener phase noise" by T. Pollet et al. On Commun.G Vol. Was published on 34. According to this paper, for frequency offset detection in an OFDM system, the method uses an analysis under the assumption that the frequency offset is very small and can be applied in an OFDM WLAN system.

More specifically, according to the above paper, a signal generated at the transmitter is received at the receiver through a multipath channel and an additive white gauge noise (AWGN) channel, and the received signal is randomly normalized through a mismatch emulator. The frequency offset of the signal that is distorted at the frequency offset of and is distorted by the arbitrary frequency offset is estimated by a frequency offset estimator using a short preamble and a long preamble. In this case, the frequency offset synchronization is divided into two parts, a coarse frequency offset estimation method and a fine frequency offset estimation method, and the performance of the frequency offset initial synchronization is a given frequency offset and estimated frequency in a test. It can be evaluated as Mean Square Error (MSE) between offsets. Here, the number of moving averages during frequency offset estimation plays an important role in analyzing the performance of the initial frequency offset synchronization. In this paper, we propose an analytical method for this frequency offset and a simple technique using analysis under the assumption that the frequency offset is very small.

On the other hand, CCK (complementary code keying) is a DSSS coding scheme used in the 802.11b WLAN standards of 5.5 and 11 Mbps. The slower 1 to 2 Mbps specification uses Barker coding, which provides up to 64 CCKs and overlaps transmissions using multiple different codes, whereas Barker coding provides only one coding pattern. Unlike CDMA, which uses CMC, CCK uses several different codes to serially transmit a larger amount of data in a TDM manner.

Like the other wireless communication systems, the CCK system also causes performance degradation due to differences in carrier frequencies at the transmitter and the receiver. That is, a signal-to-noise ratio (SNR) decrease occurs due to the offset of the carrier frequency, resulting in performance degradation. In addition, due to the difference in the sampling frequency (sampling frequency) at the transmitting end and the receiving end generates an offset that is an error in the sampling time, which causes a performance degradation of the CCK system. Therefore, there is a problem in that the receiver must estimate the offset of the carrier frequency and the sampling frequency and perform compensation accordingly.

In other words, although the transmitter and the receiver of the CCK wireless LAN system operate an oscillator generating the same frequency, the frequency offset may occur during the actual transmission / reception process. In addition, a frequency offset may also occur due to a Doppler shift effect in a fading channel. This frequency offset may degrade performance during accurate signal demodulation in a receiver.

An object of the present invention for solving the above problems is that the frequency offset generated during the transmission and reception of the CCK wireless LAN system and the frequency offset caused by the Doppler transition effect on the fading channel are used to improve the performance of the signal demodulation in the receiver. The present invention provides a frequency offset estimation apparatus and method for short-range wireless packet communication systems capable of deteriorating, maintaining the performance of the demodulation process, and simplifying the implementation complexity.

Frequency offset estimation method according to an aspect of the present invention for achieving the above object,

A frequency offset estimation method for a CCL (Complementary Code Keying) wireless LAN system,

a) extracting a plurality of symbols for respective paths from a signal received in a multipath, and performing a first stage compensation on the received signal with a frequency offset estimated according to an estimated phase difference between the extracted adjacent symbols; And b) extracting a plurality of symbols for each corresponding path from the signal on which the compensation of the first stage is performed, and compensating the first stage with a frequency offset estimated according to the estimated phase difference between adjacent symbols by the number of phase difference symbol estimation intervals. Performing fine compensation on this performed signal.

Here, the step a) may include extracting a symbol for each corresponding path in the preamble section of the received signal; Obtaining a complex phase difference between adjacent symbols of the plurality of symbols extracted for each path; Obtaining a sum of complex phase differences between symbols of the corresponding paths; Obtaining an average of a sum of phase differences between symbols over an entire path; Estimating a phase difference from the average value of the complex phase difference; Converting the estimated phase difference into a frequency offset; And performing compensation on the received signal through the converted frequency offset.

Also, the step b) may include extracting a symbol for each corresponding path with respect to the signal whose frequency offset of the first stage is compensated for; Extracting the symbol and obtaining a complex phase difference between adjacent symbols by the number of phase difference estimation symbol intervals; Obtaining a sum of complex phase differences between symbols of a corresponding path by the number of phase difference estimation symbol intervals; Calculating an average of a sum of phase differences between symbols by the number of phase difference estimated symbol intervals for the entire path; Estimating a phase difference from the average value of the complex phase difference; Converting the estimated phase difference into a frequency offset; And compensating for a signal whose frequency offset of the first stage is compensated through the converted frequency offset.

In addition, the extracted symbol is characterized in that the symbol is extracted by a despreading process for each corresponding path.

The sum of the phase differences may be a sum of phase differences between differential BPSK (DBSPK) symbols in a preamble period.

In addition, the estimated number of symbols in the step b) is larger than the estimated number of symbols in the step a).

Further, in the step b), the average number of the phase difference is adjusted according to the value of the phase difference estimation symbol interval.

Frequency offset estimation apparatus according to another aspect of the present invention,

A frequency offset estimation apparatus for a wireless LAN system of CCK (Complementary Code Keying) method,

A frequency offset estimator of a first stage that extracts a plurality of symbols for each path from a signal received in a multipath and compensates the received signal with a frequency offset estimated according to the estimated phase difference between the extracted adjacent symbols. ; And extracting a plurality of symbols for each corresponding path from the signal whose frequency offset is compensated by the frequency offset estimator of the first stage, and using the frequency offset estimated according to the estimated phase difference between adjacent symbols by the number of phase difference symbol estimation intervals. The frequency offset estimator of the first stage includes a frequency offset estimator of the second stage that compensates for the signal whose frequency offset is compensated.

Here, the frequency offset estimation unit of the first stage, the symbol extractor for extracting for each path of the preamble section of the received signal; A phase corrector for obtaining a complex phase difference between adjacent symbols for a predetermined number of symbols extracted for each path; A phase difference adder for respectively calculating the sum of the complex phase differences between symbols of the corresponding paths; A phase difference averager for obtaining an average of a sum of phase differences between symbols over an entire path; A phase difference detector for estimating a phase difference from the average value of the complex phase differences; A frequency estimator for converting the estimated phase difference into a frequency offset; And a frequency offset compensator configured to compensate for the frequency offset with respect to the received signal through the converted frequency offset.

The frequency offset estimation unit of the second stage may include: a symbol extractor that extracts a symbol for each path of a signal whose frequency offset is compensated by the frequency offset estimation unit of the first stage; A phase corrector for extracting the complex and obtaining a complex phase difference between adjacent symbols by the number of phase difference estimation symbol intervals; A phase difference adder for obtaining a sum of complex phase differences between symbols of a corresponding path by the number of phase difference estimation symbol intervals; A phase difference averager that obtains an average of the sum of phase differences between symbols by the number of phase difference estimated symbol intervals for the entire path; A phase difference detector for estimating a phase difference from the average value of the complex phase differences; A frequency estimator for converting the estimated phase difference into a frequency offset; And a frequency offset compensator configured to compensate the frequency offset with respect to the signal whose frequency offset is compensated in the frequency offset estimator of the first stage through the converted frequency offset.

Hereinafter, an apparatus and method for frequency offset estimation for a short range wireless packet communication system according to an exemplary embodiment of the present invention will be described in detail.

1 is a view for explaining the structure and position of the demodulator structure and the frequency offset estimator in a wireless LAN system of the CCK (Complementary Code Keying) method according to an embodiment of the present invention.

Referring to FIG. 1, in a CCK-type wireless LAN system according to an embodiment of the present invention, a demodulator structure and a frequency offset estimator include an analog / digital converter (ADC) 12 after a received packet signal is amplified by an amplifier 11. Is converted into a digital signal by using the automatic gain control unit 13.

In addition, the multi-path acquiring unit 15 is operated by the enable signal detected by the signal detector 14 to check whether the received packet signal is multi-path from the digital signal. The estimator 16 estimates the frequency offset of the received packet signal for the multipath.

Thereafter, the frequency offset is input to the demodulator 20 by multiplying the estimated signal component with the digital signal through a multiplier 17, which is a channel matched filter (CMF) 21, a switch 22 and a determination. The demodulator 20 including a feedback feedback equalizer (DFE) 23 undergoes a demodulation process on the received packet signal through down sampling using a demodulation algorithm. At this time, the demodulator 20 performs a demodulation process using the channel coefficients for the digital signal in the channel coefficient estimator 18.

The frequency offset estimation algorithm according to an embodiment of the present invention has a structure of measuring average frequency offset between symbols of a received packet in a WLAN system of a complementary code keying (CCK) scheme and performing compensation for it. This means that if two transmitted identical symbols pass through the channel, the two symbols will have almost the same frequency offset, so the PN code applied to the spread signal generation will be spread out. offset) and estimate the frequency offset from this phase offset to compensate for the frequency offset for the received packet.

2 is a diagram illustrating a received signal model based on a frequency offset in consideration of a transmission signal and a channel according to an embodiment of the present invention.

)을 다음의 [수학식 1]과 [수학식 2]와 같이 설계한다고 가정한다.Referring to FIG. 2, first, a packet transmitted from the transmitter 25 (

) Is designed as shown in [Equation 1] and [Equation 2] below.

,

,

은 샘플 인덱스(sample index)를 나타낸다.here,

Represents a sample index.

은 송신 패킷의 총 샘플 수를 나타낸다.here,

Represents the total number of samples of the transmission packet.

)은 다음과 같이 [수학식 3]과 같은 형태로 수신기(28)에 수신된다. 즉, 채널에 의해 발생한 주파수 오프셋에 의해 변형된 송신 패킷 벡터 신호(T_f[n])은,The outgoing packet across the channel is then

) Is received by the receiver 28 in the form as shown in [Equation 3] as follows. That is, the transmission packet vector signal T _f [n] modified by the frequency offset generated by the channel is

,

,

이고,

는 샘플 인덱스(sample index)이다. 따라서 상기 수신기(28)에서의 수신 패킷( R ( n ))은,This is

ego,

Is a sample index. Therefore, the received packet R ( n ) at the receiver 28 is

)는 신호의 과도-샘플링 인수(over-sampling factor:

)와 패킷의 전송 속도를 곱한 값이고, W[n]은 부가적인 백색 가우시안 잡음(AWGN: Additive White Gaussian Noise)을 나타낸다. 상기 수신기(28)에서는 이러한 수신 패킷들( R ( n ))이 페이딩(fading) 채널에 의해 다중경로로 수신되며, 각 경로들에 대한 주파수 오프셋의 평균값 추정이 이루어져야 한다. 도 2에서, 도면부호 26은 채널에 의해 발생한 주파수 오프셋 성분을 나타내며, 도면부호 27은 송신 패킷 신호 벡터(

) 및 부가적인 백색 가우시안 잡음 벡터 W(n)가 더해지는 가산기를 나타낸다.It looks like this, where the carrier frequency (

) Is the over-sampling factor of the signal.

Multiplied by the transmission rate of the packet, and W [n] represents Additive White Gaussian Noise (AWGN). In the receiver 28, these received packets R ( n ) are received in a multipath by a fading channel, and an average value estimation of frequency offsets for each path should be made. In Fig. 2, reference numeral 26 denotes a frequency offset component generated by a channel, and reference numeral 27 denotes a transmission packet signal vector (

) And an additional white Gaussian noise vector W (n).

As described above, the transmitter 25 and the receiver 28 operate as oscillators generating the same frequency, but in actual transmission and reception processes, frequency offset may occur due to frequency instability of the oscillator during each transmission and reception period. In addition, the frequency offset may also occur due to the Doppler shift phenomenon in the fading channel.

This frequency offset acts as a factor in making accurate signal demodulation at the receiver 28 difficult, and therefore, the receiver 28 needs an algorithm to compensate for this frequency offset phenomenon. In this case, the frequency offset estimation algorithm estimates the frequency offset and performs a process of minimizing the frequency offset of the received signal through the estimated frequency offset.

3 is a diagram illustrating a structure of a frequency offset estimator for a CCK wireless LAN system according to an embodiment of the present invention.

및 제2단의 주파수 오프셋 추정기로부터 보상된 신호

가 출력되게 된다.Referring to FIG. 3, according to an embodiment of the present invention, two frequency offset estimation is performed, and a signal compensated from the frequency offset estimator of the first stage with respect to the received signal r ( n ) .

And a signal compensated from the frequency offset estimator of the second stage

Will be output.

개의 심볼을 추출하게 되며, 위상 수집부(315)에 의해 해당 경로별로 추출된 소정 개수의 심볼에 대해 인접 심볼간 복소수 위상차를 구하게 된다.As shown in FIG. 3, the frequency offset estimator according to the embodiment of the present invention, for the received signal r ( n ) , first through the first path 310 to the K-th path 320 in the first stage, respectively. The barker code spreader 311 performs a despreading process for each path in the preamble section of the received signal.

Symbols are extracted, and a complex phase difference between adjacent symbols is obtained for a predetermined number of symbols extracted for each path by the phase collector 315.

In addition, the sum of the complex phase differences between the symbols of the corresponding path is calculated by the phase difference adder 316, and the average of the sum of the phase differences between the symbols is calculated for the entire path by the phase difference averager 321.

In addition, the phase difference detector 322 estimates the phase difference from the average value of the complex phase difference, and the frequency estimation unit 323 converts the estimated phase difference into a frequency offset, and then a numerically controlled oscillator (NCO). 324 approximately compensates for the frequency offset with respect to the received signal through the estimated frequency offset.

The frequency offset estimator of the second stage includes a Barker code spreader 331, a phase collector 337, a phase difference adder 338, a phase difference averager 341, a phase difference detector 342, and a frequency estimator 343. ) And NCO 344, and operate similar to the above-described components of the first stage through the first path 330 to the K-th path 340. Here, reference numerals 313 and 335, which are not described, denote complex phases, respectively, reference numerals 314, 325, 336, and 345 denote multipliers, and reference numeral 312 denotes delay of the first symbol interval, reference numerals 332, 333. And 334 represents a delay of L symbol intervals.

The frequency offset estimation method according to an embodiment of the present invention performs a two-step frequency offset estimation and compensation process on the received signal r ( n ), which will be described in detail with reference to FIG. 3.

First, referring to the operation of the frequency offset estimation apparatus of the first stage, the symbol is extracted by the decoupling process for each path by the Barker code spreader 311 for the preamble section of the received signal r ( n ) . .

는 k번째 다중경로의 지연 시간을 의미하고,

은 11-칩(chip)에 해당하는 심볼 주기, K는 총 경로수를 의미한다. 또한,

는 11-칩 바커 코드(Barker code) 시퀀스를 나타낸다. 이와 같이, 해당 경로별로

개의 심볼을 추출하고, 인접 심볼간 위상차를 전체 경로에 대하여 평균하면 다음과 같다.here,

Is the delay time of the kth multipath,

Denotes a symbol period corresponding to an 11-chip, and K denotes a total number of paths. Also,

Denotes an 11-chip Barker code sequence. Like this,

Symbols are extracted and the phase difference between adjacent symbols is averaged over the entire path as follows.

는 k번째 경로의 N개 심볼에 대한 위상차의 합을 의미하며,

는 K개의 모든 경로에 대한 위상차의 평균을 의미한다. 상기

값은 프리앰블 구간의 심볼, 즉, DBSPK(Differential BPSK) 심볼간 위상차의 합이 되는데, 상기 주파수 오프셋에 의해 영향을 받은 정확한 위상차를 추정하기 위해서, 성상도 상의 두 심볼 위치 중 하나는 π만큼의 위상 보정(Phase Correction)이 이루어져야 한다. 이러한 위상 보정을 적용한 수학식 6의 결과는 복소수 값을 갖는 위상차가 되며, 이러한 복소수 결과로부터 다음과 같이 위상차를 추정하게 된다.here,

Is the sum of the phase differences for the N symbols of the k-th path,

Denotes an average of phase differences for all K paths. remind

The value is the sum of the phase differences between the symbols in the preamble interval, that is, the differential BPSK (DBSPK) symbols. In order to estimate the exact phase difference affected by the frequency offset, one of the two symbol positions in the constellation is equal to π phases. Phase correction should be made. The result of Equation 6 to which the phase correction is applied becomes a phase difference having a complex value, and the phase difference is estimated from the complex result as follows.

If the estimated phase difference is converted to a frequency offset,

는 11-칩 구간에 해당하는 한 개의 심볼 주기를 의미한다. 상기 수학식 8과 같이 추정한 주파수 오프셋을 통해, 제1단에서는 최종적으로 수신 신호에 대해 주파수 오프셋 보상 과정을 수행하게 된다.You get the same value as here,

Denotes one symbol period corresponding to the 11-chip interval. Through the frequency offset estimated as shown in Equation 8, the first stage finally performs a frequency offset compensation process on the received signal.

만큼 주파수 오프셋이 보상된 신호

에 대하여, 수학식 5의 방식과 같이 역확산 과정을 수행하여 심볼을 추출해 낸다.Next, in the second stage,

Signal with frequency offset compensated for

For, extract the symbol by performing the despreading process as in the equation (5).

Therefore, in the same manner as in Equation 10, after N 'symbols are extracted and L (L <N') phase differences between symbols are obtained, the average of the phase differences over K total paths is as follows.

는 위상 보정된 k번째 경로의 L개 심볼간 복소수 위상차의 합을 의미하며,

는 K개의 모든 경로에 대한 L개 심볼간 위상차의 평균을 의미한다.At this time, as in Equation 6,

Denotes the sum of the complex phase differences between the L symbols of the k-th path with phase correction,

Denotes an average of phase differences between L symbols for all K paths.

Therefore, the phase difference is estimated from the averaged complex phase difference of Equation 11 as shown in Equation 7 of the first stage.

에 대하여 다음과 같이 주파수 오프셋 보상 과정을 수행한다.The phase difference thus estimated is converted into a frequency offset, which is compensated from the first stage.

For the frequency offset compensation process is performed as follows.

는 11-칩 구간에 해당되는 L개의 심볼 주기를 의미한다. 따라서 수학식 13의

은 수신 신호 r ( n )이 2단계의 주파수 오프셋 추정 알고리즘을 통해 보상된 최종 형태가 된다.here,

Denotes L symbol periods corresponding to 11-chip intervals. Therefore, the equation

Is the final form in which the received signal r ( n ) is compensated through a two-step frequency offset estimation algorithm.

As described above, the reason why the frequency offset estimation algorithm is divided into two stages is to reduce the large frequency offset portion through coarse estimation during the small estimated symbol interval N in the first stage. The second stage is to design a function of minimizing the frequency offset by performing more precise fine estimation.

Therefore, the estimated number of symbols N 'in the second stage has a larger value than the estimated number of symbols N in the first stage, and also controls the value of the phase difference estimation symbol interval L in the second stage. This also affects the average number of phase differences. In view of this, the estimated number of symbols N in the first stage, the estimated number of symbols N 'in the second stage, and the phase difference estimation symbol spacing in the second stage so that the residual frequency offset can be minimized. The choice of (L) is essential.

4 is a performance analysis diagram of a frequency offset estimation algorithm for a CCK wireless LAN system according to the present invention. In order to analyze the performance of the frequency offset estimation algorithm according to the present invention, a frequency offset of 120 kHz is applied to a received packet. The average frequency error between the frequency offset set and the frequency offset estimated by the algorithm is expressed in ㎐ units. By setting two multipaths with 2-chip path delays, two estimation processes are performed for each path in the first and second stages, and the number of estimated symbols in the first stage is set to 3, and the second The number of symbols at the stage was set to 11. In addition, the phase error estimation symbol interval in the second stage is set to five symbols to perform six averaging processes.

As a result, as shown in the performance curve of FIG. 4, it can be seen that as the SNR improves, a trend closer to the frequency offset given by the estimated frequency offset value is obtained. Able to know. This degree of frequency offset is an error that can be overcome by the phase tracking algorithm in the demodulation process. If the estimated number of symbols applied is increased, more accurate estimation can be made.

Meanwhile, the frequency offset estimation method according to an embodiment of the present invention as described above is implemented as a program and stored in a recording medium (CD-ROM, RAM, ROM, floppy disk, hard disk, magneto-optical disk, etc.) in a computer-readable form. Can be.

Although the preferred embodiment of the present invention has been described in detail above, the present invention is not limited thereto, and various other changes and modifications are possible.

According to the present invention, performance can be maintained in the accurate signal demodulation process in the receiver of the CCK-type wireless LAN system, and the complexity of the implementation can be simplified.

Claims (10)

In the frequency offset estimation method for a wireless LAN system of the CCK (Complementary Code Keying) method, a) extracting a plurality of symbols for respective paths from a signal received in a multipath, and performing a first stage compensation on the received signal with a frequency offset estimated according to an estimated phase difference between the extracted adjacent symbols; And b) extracting a plurality of symbols for each path from the signal on which the compensation of the first stage is performed, and compensating the first stage with a frequency offset estimated according to the estimated phase difference between adjacent symbols by the number of phase difference symbol estimation intervals; Performing a second stage compensation on the performed signal Frequency offset estimation method comprising a. The method of claim 1, Step a) is Extracting a symbol for each corresponding path in the preamble section of the received signal; Obtaining a complex phase difference between adjacent symbols of the plurality of symbols extracted for each path; Obtaining a sum of complex phase differences between symbols of the corresponding paths; Obtaining an average of a sum of phase differences between symbols over an entire path; Estimating a phase difference from the average value of the complex phase difference; Converting the estimated phase difference into a frequency offset; And Performing frequency offset compensation on the received signal through the converted frequency offset Frequency offset estimation method comprising a. The method of claim 1, B), Extracting a symbol for each corresponding path with respect to the signal on which the compensation of the first stage is performed; Extracting the symbol and obtaining a complex phase difference between adjacent symbols by the number of phase difference estimation symbol intervals; Obtaining a sum of complex phase differences between symbols of a corresponding path by the number of phase difference estimation symbol intervals; Calculating an average of a sum of phase differences between symbols by the number of phase difference estimated symbol intervals for the entire path; Estimating a phase difference from the average value of the complex phase difference; Converting the estimated phase difference into a frequency offset; And Performing frequency offset compensation on the signal on which the compensation of the first stage is performed through the converted frequency offset Frequency offset estimation method comprising a. The method according to claim 2 or 3, The extracted symbol is a frequency offset estimation method characterized in that the symbol is extracted by the process of despreading for each path. The method according to claim 2 or 3, And the sum of the phase differences is a sum of phase differences between differential BPSK (DBSPK) symbols in a preamble section. The method of claim 1, And the estimated number of symbols in step b) is greater than the estimated number of symbols in step a). The method of claim 1, And in step b), the average number of phase differences is adjusted according to the value of the phase difference estimation symbol interval. In the frequency offset estimation apparatus for a wireless LAN system of CCK (Complementary Code Keying) method, A frequency offset estimator of a first stage that extracts a plurality of symbols for each corresponding path from a signal received in a multipath and compensates for the received signal with a frequency offset estimated according to the estimated phase difference between the extracted adjacent symbols. ; And The first frequency offset estimator extracts a plurality of symbols for each corresponding path from the signal whose frequency offset is compensated for, and uses the first frequency offset estimated according to the estimated phase difference between adjacent symbols by the number of phase difference symbol estimation intervals. The frequency offset estimator of the second stage which compensates the signal whose frequency offset is compensated in the frequency offset estimator of the stage Frequency offset estimation apparatus comprising a. The method of claim 8, The frequency offset estimation unit of the first stage, A symbol extractor for extracting the preamble section of the received signal for each corresponding path; A phase corrector for obtaining a complex phase difference between adjacent symbols for a predetermined number of symbols extracted for each path; A phase difference adder for respectively calculating the sum of the complex phase differences between symbols of the corresponding paths; A phase difference averager for obtaining an average of a sum of phase differences between symbols over an entire path; A phase difference detector for estimating a phase difference from the average value of the complex phase differences; A frequency estimator for converting the estimated phase difference into a frequency offset; And A frequency offset compensator that compensates for the frequency offset with respect to the received signal through the converted frequency offset Frequency offset estimation apparatus comprising a. The method of claim 8, The frequency offset estimation unit of the second stage, A symbol extractor for extracting a symbol for each path of a signal whose frequency offset is compensated by the frequency offset estimator of the first stage; A phase corrector for extracting the complex and obtaining a complex phase difference between adjacent symbols by the number of phase difference estimation symbol intervals; A phase difference adder for obtaining a sum of complex phase differences between symbols of a corresponding path by the number of phase difference estimation symbol intervals; A phase difference averager that obtains an average of the sum of phase differences between symbols by the number of phase difference estimated symbol intervals for the entire path; A phase difference detector for estimating a phase difference from the average value of the complex phase differences; A frequency estimator for converting the estimated phase difference into a frequency offset; And A frequency offset compensator for compensating a frequency offset with respect to a signal whose frequency offset is compensated in the frequency offset estimator of the first stage through the converted frequency offset Frequency offset estimation apparatus comprising a.

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